The 2D-coordinates of the \(\gamma \) -ray interaction in the transverse \(xy\) -plane of each PSD in i-TED is accomplished by fitting, on an event-by-event basis, the analytical expression of Li et al. [1]} to the SiPM charge response of each PSD, in a similar fashion as reported in Ref. [2]}. After a careful characterization of all detectors, spatial resolutions of around 1 mm fwhm were found for the 10 mm and 25 mm thick crystals at 511 keV. The third space coordinate \(z\)  or depth-of-interaction in each crystal is obtained from an empirical parameterization of the SiPM response at half-height of the maximum[3]}. In the latter case, typical uncertainties between 4 mm and 5 mm are obtained. The field of view in which the PSD has a linear response was determined to be of around 20 cm\(^2\) , which corresponds to about 80% of the crystal base surface [2]}.
<FIGURE>